1. Field of the Invention
The present invention relates to a novel pigment, which produces a color through the light interference as well as the light scattering, and a process for producing the same. In accordance with the present production process, the novel pigment can be produced in a stable color tone.
2. Description of Related Art
A pearl mica pigment has been known so far in which titanium dioxide is coated on a surface of mica. The pearl mica pigment produces a pearl-like color tone through light interference, and it is possible to obtain various interference colors by varying the thickness of the titanium dioxide layer. Further, Japanese Unexamined Patent Publication No. 78265/1984 discloses a pearl mica pigment having an improved weather resistance in which chromium compound is deposited on a surface of a titanium dioxide layer of the pearl mica pigment. Furthermore, Japanese Examined Patent Publication No. 3345/1985 discloses a pigment in which micaceous particles are treated with a solution containing tin compound, the micaceous particles are coated with titanium dioxide, and the micaceous particles are further treated to include chromium hydroxide on the surface.
However, a paint employing the pearl mica pigment does not give a metallic glossy effect, and is not a satisfactory metallic paint. Further, when compared with a metallic paint film containing an aluminum powder, the paint film containing a pearl mica pigment is inferior in the so called "flip-flop characteristic." Here, an inferior "flip-flop characteristic" means that a paint film exhibits small difference between the brightness when viewed at the front and the brightness when viewed diagonally.
Hence, the inventors of the present invention applied for a patent for a novel pigment under Japanese Patent Application No. 265795/1987. The novel pigment comprises a pearl mica pigment or a pearl mica pigment including chromium compound, and a metallic glossy dots including metal (such as silver) or alloy, formed on a surface of the pearl mica pigment or the like in a scattering manner and occupying 0.05 to 95% of the total surface area of the pearl mica pigment or the like. A metallic paint film containing the novel pigment gives a glossy effect resulting from the glossy dots, and produces an interference color resulting from the light interference and a scattering color resulting from the reflection and the scattering. Also, the metallic paint film is superior in the "flip-flop characteristic."
In the course of the development of the novel pigment, the inventors of the present invention found that some of the thus produced novel pigments exhibited varying colors, and that the colors varied considerably when the glossy dots occupied less surface area of the novel pigments in total. The inventors accordingly investigated the cause through an observation with microscope or the like, and discovered the following. When forming the glossy dots in a scattering manner, the distribution and the particle diameters of the glossy dots deviate, and adversely affect the reflection and the scattering of light, thereby varying the interference colors. As a result, the novel pigments exhibit varying colors.